JPH01136905A - Method for joining ferrous member - Google Patents

Abstract

PURPOSE:To execute joining of good ferrous member without any changing the quality of the main part by forming graphite films on the joining surfaces of both members of ferrous sintered alloy or ingot iron and steel material produced by melting and ferrous sintered alloy, combining and heating both combined materials under non-oxidized atmosphere at the developing temp. of liquid- phase of the ferrous sintered alloy. CONSTITUTION:The graphite film is formed on each joining surface of a first member composing of the ferrous sintered alloy or the iron and steel material produced by melting, which is ferrous alloy for ordinary machining element, and a second member composing of the ferrous sintered alloy containing C, P, S. Thickness of the graphite film may be at about 1-3mum. Successively, both members forming the graphite film on the joining surface area combined and are heat-treated under non-oxidizing atmosphere at the developing temp. of the liquid-phase of the second member. By this method, the good joining of both members is obtd. without any changing the quality of the main part. Further, by adopting this method to the production of the wear resistant complexed member, the excellent joining quality is obtd. at economically.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for joining iron-based members using sintering technology, and is particularly useful when manufacturing parts made of different materials, such as those for internal combustion engines. The present invention relates to a joining method suitable for manufacturing valve lifters, rocker arms, etc. of valve train mechanisms.

When joining another material such as a wear-resistant bonding alloy to the main part of steel or iron-based sintered alloy, brazing is common, but other materials such as liquid phase generated from the sintered alloy during heating are used. A method of infiltrating a sintered material with copper and joining with the infiltrating material, a method of forming irregularities or an appropriate trapezoidal shape on the base material and the members to be joined, and joining by plastic working, and a method of joining by plastic working. There is also a method of fitting in a similar manner and utilizing thermal deformation to achieve tight fit and connection.

By the way, in general, compared to joining each member in a tight state, when joining in a laminated state, unless the joining is more perfect, the members will easily separate due to repeated loads.

However, in the prior art, mechanical joining methods that provide unevenness that fits into the laminated joint surfaces are applicable to small loads, but are insufficient for machine elements that are subjected to high loads or shock-resistant loads. be.

In this regard, brazing has high bonding strength and good bonding reliability, but the filler metal infiltrates into the pores of the sintered metal parts, requiring a large amount of filler metal, changing the properties of the sintered material, and reducing workability. There are pros and cons to being bad.

The infiltration bonding method is similar to the above, and is good if sealing is expected with the infiltration material, but it has the disadvantages that infiltration changes the properties of the sintered alloy and requires a large amount of material, increasing costs. .

In addition, although bonding methods that utilize the liquid phase of sintered alloys have good productivity, the amount of liquid phase is small, so the surface roughness of the bonded surface is large, and if there are gaps, the bond may be incomplete. If the carbon d of the base member and the bonding member are different, there is a problem that the carbon moves during heating and the main part of the member changes in quality.

This invention is an improvement on the above-described joining method using the liquid phase of sintered materials, and the gist of this invention is as described in Section 1. The method is characterized in that after a graphite coating is formed on the joint surface of the second member, each member is assembled and heated in a non-oxidizing atmosphere.

The structure and operation of the present invention will be explained below.

First, the first member forms the main body of the part and is made of a ferrous sintered alloy or a melted steel material. This member is made of common hypoeutectoid carbon steel 9 alloy steel, heat-resistant steel, etc., or a similar sintered alloy, and is made of an iron alloy for ordinary machine elements.

Next, the second member is made of a metal carbide precipitation hardening iron-based sintered alloy with excellent wear resistance that generates a liquid phase at normal sintering temperatures. The gist of this invention is that if the iron-based alloy produces a liquid phase,
Although it exhibits a similar effect, this sintered material is selected because it has a specific industrial application and is the most effective combination of materials.

In this type of alloy, P is an element that contributes to liquid phase formation. In addition, B, Sn, CLJ, etc. may be added. Further, this alloy contains about 1 to 4% carbon, which combines with Fe and carbide-forming elements. Cr is an essential element as a carbide-forming element, and Cr also dissolves in the iron matrix and contributes to wear resistance.

Similarly, MO, W, V, etc. may be included as elements that form carbides. Further, the second member may be a compacted powder or a sintered body.

Therefore, the inventor conducted the following experiment.

As described above, when the first member and the second member are joined by the conventional method, that is, stacked as they are and heated in a reducing gas at the liquid phase generation temperature of the second member, sintering progresses and the liquid phase changes to the second member. The mating surfaces of the members are wetted and the carbon diffuses from the second member to the first member.

However, when we investigated the situation near the joint and each member after cooling, we found that according to the conventional method, a long and narrow gap remained at the joint due to the small amount of liquid phase, and the second member It was found that the hardness decreased due to decarburization, and that the portion of the first member near the joint had a carburized structure.

In contrast, the method of the present invention forms a graphite coating on the joint surfaces of both members before heating. Therefore, graphite generates an additional liquid phase at the joint and also has the effect of preventing decarburization of the second member. In addition, this graphite film is created by coating or spraying a paint containing colloidal graphite dispersed in a dispersion medium such as water or alcohol containing appropriate dispersants, viscosity enhancers, antifoaming agents, etc., and then drying it. It can be obtained by The thickness of the coating film is preferably about 1 to 3 μm. If the coating film is too thick, a large amount of cementite will precipitate on the joint surface, and unreacted graphite will remain, making fatigue failure more likely.
If the thickness is below, the bonding effect will be poor, so the thickness of the graphite coating in the present invention is preferably about 1 to 3 μm.

In this way, the characteristics of the joined parts obtained by the method of the present invention are as follows:
Its cross section can be observed under a microscope. As a result, we found that the vicinity of the joint of the first member has a carburized structure, that the second member has almost no decarburization and has a uniform composition, and that the joint has few pores and the amount of carbon therein. It could be observed that the number was the same or slightly higher than that near the second phase joint.

Next, an embodiment of the present invention will be described in comparison with a conventional method.

A 0.2% C carbon steel for mechanical structures was prepared as the first member, and the surfaces to be joined were ground with a surface grinder.

As a second member, Fe-C-Cr-Mo-W-V-based atomized alloy iron powder, Fe-P alloy powder, and graphite powder were prepared, and the overall composition was 5% Cr-1,5 by weight. %C-
The mixture was blended to become 3% MO, 3% W, 2% V, and 1.1% P, and an additional 1% of zinc stearate was added to form a mixed powder, which was then pressed into a predetermined shape at a compacting pressure of 6 t/cM. After, temperature 1
Sintering was carried out in a decomposed ammonia gas atmosphere furnace at 000'C. The joint surface of this sintered body was also polished in the same manner as the first member.

On one side of the second member, a water-dispersed colloidal graphite film was applied to the joint surface and dried to form a graphite film with a roughness of 2 μm (the present invention). Furthermore, the other one is a sample that has only been polished and belongs to the conventional method.

Therefore, the first member and the second member were brought into contact with their joint surfaces and heat-treated in a decomposed ammonia gas atmosphere furnace at a temperature of 1150°C. The cross-sectional microstructure and carbon content of each sample obtained were examined.

As a result, when using the bonding method according to the present invention in which a graphite coating was applied, there were few holes in the bonded part of the sample, and the bonding was good, whereas when using the conventional bonding method, there were no gaps between the two parts. It was recognized that there was a gap.

Further, FIG. 1 is a graph showing the amount of carbon near the joint according to the above experiment, in which the joining method according to the present invention is shown by a solid line, and the conventional method is shown by a dotted line. As is clear from this graph, the carburization depth of the first member is approximately 1.5 mm, which is slightly greater in the present invention. Further, it is recognized that the amount of carbon in the second member is gradually decarburized in the case of the conventional method, and it is found that the amount of carbon in the second member is hardly decarburized in the method of the present invention.

As is clear from the above experimental results, according to the joining method according to the present invention, good joining can be obtained without changing the material of the main parts, and this can be applied to the manufacturing method of wear-resistant composite parts. If adopted, it is possible to obtain economical and excellent bonding quality.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the amount of carbon in the cross section of the joined parts. Patent applicant Hitachi Powder Metallurgy Co., Ltd.

Claims (1)

[Claims] The first member is made of a ferrous sintered alloy or molten steel material,
In a jointed part in which the second member is made of an iron-based sintered alloy containing at least C, P, and Cr, a graphite coating film is formed on the joint surfaces of the above-mentioned two members, and then both members are combined, and the second member is assembled in a non-oxidizing atmosphere. A method for joining iron-based members, characterized by heating at a liquid phase generation temperature.